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HEVT Cleantech “Breakthrough”: Switched Reluctance or Electric Motor Hype

November 12, 2012 2 Comments
HEVT Hybrid Electric Vehicle Technologies Inc. switched reluctance SR electric motor

HEVT – Hybrid Electric Vehicle Technologies Inc. switched reluctance electric motor (internal stator view)

Congratulations to Hybrid Electric Vehicle Technologies (HEVT), on winning the $250k grand prize at the 2012 Cleantech Open in San Jose, based on their work with switched reluctance motor technology. When the competition bills itself “The Academy Awards of Cleantech” you have to be a bit careful not to get swept up in some of the hype so that you actually miss what’s significant.  It seems like most of the media stories I’ve seen kind of miss the point on this.

One said, “HEVT is developing switched reluctance electric motor technologies that can be manufactured without using rare earth metals”. While that sounds great it’s pretty much the same as me claiming “I’ve developed a recipe for lemon-aid that can be made without using watermelons”. You see, switched reluctance motors by design are made using only lamination steels and copper wire coils — no magnets of any kind. Above is an interior photo of an HEVT motor and the graphic below shows the motor’s lamination steel construction.

HEVT Switched Reluctance SR Motor stator and rotor laminations

HEVT Switched Reluctance SR Motor stator and rotor laminations

Another story heralded “Breakthrough Electric Motor … HEVT is developing electric motor technologies that don’t depend on rare earth metals”. But that’s also confusing because AC induction motors and wound-field DC motors don’t use any magnets either and even most permanent magnet DC motors don’t use rare-earth magnets. While I’d say most brushless DC motors use rare earth magnets, that’s not a necessity.

You might be surprised to learn that switched reluctance motors were invented almost 175 years ago when around 1838 two unrelated inventors, W.H. Taylor and Robert Davidson, filed two separate unrelated patents that were based on the switched reluctance principle. The switched reluctance principle, by the way, takes advantage from the fact that an electromagnetic system always tries to adopt the geometrical configuration corresponding to the minimum reluctance of the magnetic circuit. What Taylor and Davidson did was develop devices with continuous movement as a result of the magnetic reluctance principle. The graphic below shows it in action much better than I can explain it.

switched reluctance motor

Switched Reluctance Motor

While the switched reluctance motor is theoretically the least expensive design to build it seems to have always been dragged down with baggage relating to the cost of the electronic control required to commutate it and make it run, noise, and other issues. Whenever there is an energy crunch, the topic of switched reluctance always seems to come back.

Back in the 1990s, Warner Electric made switched reluctance motors that were used by Ford Motor Company in cruise controls, Hewlett-Packard used them in some plotters and the high-efficiency Maytag Neptune front-loading washing machine used switched reluctance motors when it was introduced in 1997 but after a few years switched back to a conventional AC induction motor. In 1994, Emerson Electric acquired the U.K. company, Switched Reluctance Drives Ltd. which had done most of the switched reluctance motor work that was commercialized at the time but even with the resources of Emerson it never seemed to take off.

More recently, Sir James Dyson and his vacuum cleaner company developed high speed switched reluctance motors, claimed to be “the fastest motor in the world” (104,000 rpm).

Dyson switched reluctance motor on left

Dyson switched reluctance motor on left

The point of this post being that sometimes what’s old is new. While switched reluctance motor technology has been around a long time and many have worked with it, I would imagine that what HEVT is doing that warranted their grand prize win is more focused on reducing the complexity and cost of the control while possibly also utilizing software to overcome some of the previous obstacles to the widespread acceptance of switched reluctance motors. When I get a chance to talk to HEVT I’ll report back.

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About the Author:

John Morehead is an experienced marketing, sales and business development leader. He’s passionate about motion control and advanced motor technology and shares that enthusiastically with those he encounters and many more through his myriad marketing initiatives. This blog is one more tool to be able to spread the word about news, information and insights on the motion control, electric motors, drives and automation fields. Your comments or questions on posts are welcome.

Comments (2)

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  1. John – Thanks for clearing this up. So many sales execs hide behind techno-speak and it’s refreshing to hear the straight scoop. Just the facts! – Todd

  2. John Morehead says:

    Thanks Todd, I’m taking my Jack Webb hat off now.

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